Conventional binoculars require optics, which have both a wide-field of view and relatively high magnification. In addition, the optical design must produce an image that is correctly oriented (right-side up) with respect to the scene that is being viewed. Various image enlargement devices and techniques have been available for many years, but all conventional arrangements have drawbacks. For example, the field of view of certain telescopes is limited to the diameter of the objective lens. Thus, it cannot simultaneously have a wide field-of-view and high magnifying power. Other telescopes allow for both a wide field of view and high magnifying power, but the image is inverted.
In order to solve the problem of an inverted image, many binoculars use an additional set of lens to invert the image. Other devices include use a reflective surface to invert the image. Some devices use reflective surfaces at right angles. The double reflection introduced by the reflecting surfaces causes an inversion of an image about a single axis. Typically a pair of right angle prisms is placed between the objective lens and the eyepiece in the telescope image enlargement optics. One prism inverts the image around the horizontal axis, the second prism inverts the image around the vertical axis. As a result the image viewed in the eyepiece is correctly oriented. One problem associated with a pair of right angle prisms is that they must be oriented at right angles relative to each other to provide proper image erection. As a result it is difficult to use them in a compact binoculars.
The configurations described above have the problem that the optical axis does not lie in a single plane. Although it is possible to tilt a prismatic optical system within the binocular case to keep the optical axis in a single plane, this type of configuration results in much unused volume making it difficult to create a compact binoculars.
Another device used in binoculars is the roof prism. The optical axes of light entering and leaving the prism are collinear. The roof prism provides inversion about the horizontal axis, and the other two reflecting surfaces provide inversion about the vertical axis.
Other binocular designs are compact and permit construction into cylindrical barrels whose diameter is not much larger than the objective lens. This configuration uses prisms in close proximity. However, this solution is expensive. It is noted that mirrors cannot be used in lieu of the prism since on the prism one surface serves both as a reflective surface and as a window.
Further prism optical designs use in line optical layouts. All of the prism designs suffer the same problem: Extreme accuracy is needed in fabrication of the roof prism. If the roof prism is not exactly 90 degrees then the real image formed by the objective lens will be found to be imperfect.
Most binoculars, which utilize prisms, use solid glass prisms, which are generally expensive to manufacture. Some attempts have been made to replace the prism reflecting surfaces by piano mirror reflecting surfaces. Such use of mirrors to replace the prisms became practical with the development of high-reflectivity, first surface mirrors. However, replacement of the prism surfaces with mirrors requires that the mirrors be accurately aligned. If any of the mirror surfaces are slightly misaligned relative to each other, the optical image will be slightly off-center. This problem is serious in binocular optical systems, where the images in both optical system legs must appear to fuse perfectly. A vertical image displacement of 10 milliradians is easily noticed by the average viewer. Consequently, the recommended tolerance is only 1 milliradian. An adjustment in the location and/or tip of at least one of the optical elements is generally necessary.
The manufacture of accurately aligned mirrors for replacement of prisms in binoculars remains an expensive problem. As a result binoculars remain both bulky and expensive. There is a need for a compact, inexpensive binocular arrangement, which has relatively high magnification power.
In general, in one aspect, a compact binoculars, including a housing having a base and a light tight lid, first and second molecular telescopes having an upper and a lower surface oriented within the housing in a substantially parallel configuration, wherein the first and second monocular telescopes include a shell case having a support base and a light tight cover, an objective lens, having an objective optical axis, adjustably mounted to a first side of said shell case, a magnifying eyepiece, having an eyepiece optical axis, mounted to a second side of the shell case parallel to the objective lens, a first reflective surface having a first axis perpendicular to the first reflective surface, and mounted to the second side at an angle with respect to the second side, a second reflective surface having a second axis perpendicular to the second reflective surface, and mounted to a third side of the shell case, perpendicular to the first and second sides, a roof mirror having a third reflective surface and a fourth reflective surface forming a substantially 90 degree angle, the roof mirror having a roof axis bisecting the angle and perpendicular to a line of meeting of the third and fourth reflective surfaces, wherein the roof mirror is mounted to the base of the shellcase, a guideplate mechanically coupled to the upper surfaces of the first and second monocular telescopes, a stabilizing bar mechanically coupled to the first and second monocular telescopes.
In an implementation, the optical axis, the first axis, the second axis, the roof axis, the eyepiece optical axis, and the line of meeting being in a plane so that a path of light from a distant object encounter, in sequence, the objective lens, the first reflective surface, the second reflective surface, the roof mirror, and the magnifying eyepiece.
In another implementation, the guideplate allows a first motion in a direction substantially perpendicular to the objective optical axis and the eyepiece optical axis.
In another implementation, the guideplate allows a second motion in a direction substantially perpendicular to the first motion.
In yet another implementation, the second motion comprises moving the objective lens of the first monocular telescope and the objective lens of the second monocular telescope in tandem.
In still another implementation, the first the second, the third, and the fourth reflective surfaces are first surface mirrors.
In another implementation the binoculars further include a focus mechanism mechanically coupled to the guideplate.
In another implementation the binoculars further include an eyewidth adjustment mechanism coupled to the guideplate.
In another implementation, the roof mirror further includes a glass substrate adhesively attached to an end of each of the first and second reflective surfaces.
In another implementation, the roof prism is held in position by a brace.
In another aspect, a method of manufacturing a roof mirror is featured including placing a first reflective surface and a second reflective surface on a precision fixture such that a first end of the first reflective surface meets a first end of the second reflective surface at a substantially 90 degree angle, optically checking the alignment of the reflective surfaces, applying an adhesive along a line where the first end of the first reflective surface and the first end of the second reflective surface meet, allowing the adhesive to set, verifying that the angle between the first and second reflective surfaces has remained substantially 90 degrees, applying an adhesive along a second end of the first reflective surface and a second end of the second reflective surface, wherein the second end of the first reflective surface and the second end of the second reflective surface meet at a common point, applying a substantially rectangular glass substrate to the second end of the first reflective surface and the second end of the second reflective surface, allowing the adhesive to set and optically checking the alignment of the mirrors.
In an implementation, optically checking the mirrors includes using an autocollimater.
In another implementation, applying an adhesive includes applying an ultraviolet glue.
Other features and advantages will be apparent from the following description, the accompanying drawings and the claims.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.